Phd Student, University of Nottingham, Malaysia Campus
A fluorescent probe with great tunability for biosensing application
Cancer, a life-threatening disease arises from uncontrollable cell replication. According to World Health Organization (WHO), the death rate due to cancer disease can be reduced when cancer is detected and treated in the early stage. However, current available methods (e.g. biopsy, blood test and imaging) for early cancer detection require specialist operational skills and involve much expenditure of time as well as cost. Hence, there is a need to develop new cancer screening method that can resolve these issues. Although there are more than 100 types, cancer exhibit a common feature in its ability to replicate infinitely due to high level of telomerase. Telomerase is an enzyme protein responsible to maintain chromosomal DNA length sufficient to initiate next round of replication process. In contrast, healthy cells that lack telomerase result shorter chromosomal DNA that will induce cell death as cell replication stopped. Thus, telomerase is a potential universal biomarker for early stage cancer detection. In my project, luminescent method of self-synthesized probe is employed to detect the telomerase activity. First and foremost, a DNA fragment is smartly designed to stabilize clusters of silver atoms for them to form luminescent probe, known as silver nanoclusters. Subsequently, this modified DNA fragment reacts with telomerase. An active telomerase, such as those found in cancer cells will cause the luminescent light of silver nanoclusters to turn-off. In summary, the proposed method helps to distinguish cancer cells from normal cells at very brief processing time of one hour. Manufacturing of this luminescent probe cost less than a US dollar which aids patients’ accessibility to such affordable service.
Abstract: 12 years after the introduction of DNA-templated silver nanoclusters (DNA-AgNCs), exciting progress has been made and yet we are still in the midst of trying to fully understand this nanomaterial. The prominent excellence of DNA-AgNCs is undoubtedly its modulatable emission property, of which how variation in DNA templates causes emission tuning remains elusive. Based on the up-to-date DNA-AgNCs, we aim to establish the correlation between the structure/sequence of DNA templates and emission behaviour of AgNCs. Herein, we systematically present a wide-range of DNA-AgNCs based on the structural complexity of the DNA templates, including single-stranded DNA (ssDNA), double-stranded DNA (dsDNA), triple-stranded DNA (tsDNA) and DNA nanostructures. For each DNA category, we discuss the emission property, quantum yield and synthesis condition of the respective AgNCs, before cross-comparing the impact of different DNA scaffolds on the properties of AgNCs. A future outlook for this area is given as a conclusion. By putting the information together, this review may shed new light on understanding DNA-AgNCs while we are expecting continuous breakthroughs in this field.
Pub.: 07 Oct '16, Pinned: 26 Feb '18
Abstract: Single strand DNA (ssDNA) chimeras consisting of a silver nanoclusters-nucleating sequence (NC) and an aptamer are widely employed to synthesize functional silver nanoclusters (AgNCs) for sensing purpose. Despite its simplicity, this chimeric-templated AgNCs often leads to undesirable turn-off effect, which may suffer from false positive signals caused by interference. In our effort to elucidate how the relative position of NC and aptamer affects the fluorescence behavior and sensing performance, we systematically formulated these NC and aptamer regions at different position in a DNA chimera. Using adenosine aptamer as a model, we tested the adenosine-induced optical response of each design. We also investigated the effect of linker region connecting NC and aptamer, as well as different NC sequence on the sensing performance. We concluded that locating NC sequence at 5'-end exhibited the best response, with immediate fluorescence enhancement observed over a wide linear range (1-2500 μM). Our experimental findings help to explain the emission behavior and sensing performance of chimeric conjugates of AgNCs, providing an important means to formulate a better aptasensor.
Pub.: 16 Feb '18, Pinned: 26 Feb '18
Abstract: The high affinity of Ag+ for DNA bases has enabled creation of short oligonucleotide-encapsulated Ag nanoclusters without formation of large nanoparticles. Time-dependent formation of cluster sizes ranging from Ag1 to Ag4/oligonucleotide were observed with strong, characteristic electronic transitions between 400 and 600 nm. The slow nanocluster formation kinetics enables observation of specific aqueous nanocluster absorptions that evolve over a period of 12 h. Induced circular dichroism bands confirm that the nanoclusters are associated with the chiral ss-DNA template. Fluorescence, absorption, mass, and NMR spectra all indicate that multiple species are present, but that their creation is both nucleotide- and time-dependent.
Pub.: 22 Apr '04, Pinned: 26 Feb '18
Abstract: Herein, the conformational switch of G-rich oligonucleotide (GDNA) demonstrated the obvious functional switch of GDNA which was found to significantly affect the fluorescence of the in-situ synthesized DNA/silver nanocluster (DNA-AgNC) in homogeneous solution. We envisioned that the allosteric interaction between GDNA and DNA-AgNC would be possible to be used for screening telomere-binding ligands. A unimolecular probe (12C5TG) is ingeniously designed consisting of three contiguous DNA elements: G-rich telomeric DNA (GDNA) as molecular recognition sequence, T-rich DNA as linker and C-rich DNA as template of DNA-AgNC. The quantum yield and stability of 12C5TG-AgNC is greatly improved because the nearby deoxyguanosines tended to protect DNA/AgNC against oxidation. However, in the presence of ligands, the formation of G-quadruplex obviously quenched the fluorescence of DNA-AgNC. By taking full advantage of intramolecular allosteric effect, telomere-binding ligands were selectively and label-free screened by using deoxyguanines and G-quadruplex as natural fluorescence enhancer and quencher of DNA-AgNC respectively. Therefore, the functional switching of G-rich structure offers a cost-effective, facile and reliable way to screen drugs, which holds a great potential in bioanalysis as well.
Pub.: 07 Mar '17, Pinned: 26 Feb '18
Abstract: Luminescent silver nanoclusters were anchored by designed oligonucleotides. After hybridizing with human telomerase RNA template, the luminescence of the cluster decreased linearly with respect to the concentration of the complementary strand (25-250 nM). The cluster is therefore a potential candidate for human telomerase detection.
Pub.: 23 Jan '13, Pinned: 26 Feb '18
Abstract: Telomeres facilitate the protection of natural ends of chromosomes from constitutive exposure to the DNA damage response (DDR). This is most likely achieved by a lariat structure that hides the linear telomeric DNA through protein-protein and protein-DNA interactions. The telomere shortening associated with DNA replication in the absence of a compensatory mechanism culminates in unmasked telomeres. Then, the subsequent activation of the DDR will define the fate of cells according to the functionality of cell cycle checkpoints. Dysfunctional telomeres can suppress cancer development by engaging replicative senescence or apoptotic pathways, but they can also promote tumour initiation. Studies in telomere dynamics and karyotype analysis underpin telomere crisis as a key event driving genomic instability. Significant attainment of telomerase or alternative lengthening of telomeres (ALT)-pathway to maintain telomere length may be permissive and required for clonal evolution of genomically-unstable cells during progression to malignancy. We summarise current knowledge of the role of telomeres in the maintenance of chromosomal stability and carcinogenesis.
Pub.: 20 Jan '18, Pinned: 26 Feb '18
Abstract: Telomerase is over-expressed in over 85% of all known human tumors. This renders the enzyme a valuable biomarker for cancer diagnosis and an important therapeutic target. The most widely used telomeric repeat amplification protocol (TRAP) assay has been questioned for telomerase detection. It is reported that human telomerase activity can be visualized by using primer-modified Au nanoparticles. The working principle is based on the elongated primers conjugated to the gold nanoparticle (AuNP) surface, which can fold into a G-quadruplex to protect the AuNPs from the aggregation. The developed simple and sensitive colorimetric assay can measure telomerase activity down to 1 HeLa cell µL(-1). More importantly, this assay can be easily extended to high-throughput and automatic format. The AuNP-TS method is PCR-free and therefore avoids the amplification-related errors and becomes more reliable to evaluate telomerase activity. This assay has also been used for initial screening of telomerase inhibitors as anticancer drug agents.
Pub.: 16 Nov '11, Pinned: 26 Feb '18